Widely Tunable Morphologies in Block Copolymer Thin Films Through Solvent Vapor Annealing Using Mixtures of Selective Solvents

Abstract

Thin films of block copolymers are extremely attractive for nanofabrication because of their ability to form uniform and periodic nanoscale structures by microphase separation. One shortcoming of this approach is that to date the design of a desired equilibrium structure requires synthesis of a block copolymer de novo within the corresponding volume ratio of the blocks. In this work, we investigated solvent vapor annealing in supported thin films of poly(2-hydroxyethyl methacrylate)-block-poly(methyl methacrylate) [PHEMA-b-PMMA] by means of grazing incidence small angle X–ray scattering (GISAXS). A spin-coated thin film of lamellar block copolymer was solvent vapor annealed to induce microphase separation and improve the long-range order of the self-assembled pattern. Annealing in a mixture of solvent vapors using a controlled volume ratio of solvents (methanol, MeOH, and tetrahydrofuran, THF), which are chosen to be preferential for each block, enabled selective formation of ordered lamellae, gyroid, hexagonal or spherical morphologies from a single block copolymer with a fixed volume fraction. The selected microstructure was then kinetically trapped in the dry film by rapid drying. To our knowledge, this paper describes the first reported case where in-situ methods are used to study the transition of block copolymer films from one initial disordered morphology to four different ordered morphologies, covering much of the theoretical diblock copolymer phase diagram.

Micellar‐Mediated Block Copolymer Ordering Dynamics Revealed by In Situ Grazing Incidence Small‐Angle X‐Ray Scattering during Spin Coating

“…From these preliminary observations, the preferential sequestration of PGMEA within the PMMA domains allows to understand the formation of lamellae. However, the overall quality of the BCP structure, consisting of long‐range ordered in‐plane lamellae, is rather unexpected with respect to previously reported GISAXS experiments on BCP thin films after casting, in which poorly ordered structures were observed directly after spin coating . Indeed, only few low energy dislocations sparsely distributed within the PDMSB ‐b ‐PMMA layers are observed from STEM images, making that the PDMSB and PMMA domains are separated by well‐defined flat interfaces (see Figure C).…”

Understanding Solvent Manipulation of Morphology in Bulk‐Heterojunction Organic Solar Cells

“…Further work needs to be undertaken to determine a measurable parameter, such as HSPs, to quantify the annealing solvent. Similar to the solvent mixture method, annealing the film with a mixture can also lead to a more controllable morphology …”

Laser Spike Annealing of DSA Photoresists

“…9 This work is meaningful since very often synthesis of a block copolymer with a precisely selected composition for a specific polymer is challenging especially for a bicontinuous gyroid phase, which only occurs within a narrow range of compositions. The orderorder transition of poly(2-hydroxyethyl methacrylate)-block-poly(methyl methacrylate), (PHEMA-b-PMMA) during controlled-flow solvent vapor annealing was studied.…”